Green’s Dictionary of Slang

1. (US Und.) severe interrogation of a prisoner, the ‘third degree’.

1850		(con. 1843) Melville White-Jacket (1990) 132: From the merciless, inquisitorial baiting, which sailors, charged with offences, too often experience at the mast, that vicinity is usually known among them as the bull-ring.
1933		Ersine Und. and Prison Sl.
1949		Monteleone Criminal Sl. (rev. edn).
1960		(con. 1950-1960) R.A. Freeman Dict. Inmate Sl. (Walla Walla, WA) 20: Bull-ring – a third-degree squad.

2. (Aus.) a police office.

1851		Bell’s Life in Sydney 27 Sept. 3/2: He would [...] bring her up to the bull-ring (This locality Mr Stubbs explained was the Police Office).
1851		Bell’s Life in Sydney 29 Nov. 3/1: [They] were invited to step into the George-street bull-ring to respond to a charge of street fighting.

3. (US prison) an enclosed prison exercise yard or an open space used for punishments.

1879		Nat. Police Gaz. (NY) 20 Dec. 11/3: In January 1876 [...] he made a clever attempt to escape [...] having let himself bown into the ‘bull-ring,’ [he] was engaged in sawing one of the half-inch iron bars of the window.
1908		J. Kelley Thirteen Years in Oregon Penitentiary 12: The ‘bull ring’ is the back yard, where convicts take exercise.
1927		‘Jargon of the Und.’ in DN V 440: Bull ring, A walk or circular track within prison.
1931		Irwin Amer. Tramp and Und. Sl. 40: bull ring.–The gaol or prison walk about which prisoners are made to walk as a punishment or for exercise.
1960		(con. 1950-1960) R.A. Freeman Dict. Inmate Sl. (Walla Walla, WA) 20: Bull-ring – an exercise area for inmates.
1970		(con. 1910s) Gaddis & Long Panzram (2002) 64: The bullring was not new to old-timers in the prison. Many had walked it.

4. a military training ground [ext. of SE. use; orig. that sited at Étaples, northern France, the British Army training centre during WWI].

1918		Kia Ora Coo-ee 15 Aug. 17/1: After I’d been in Hospital for about three weeks, they treated me pretty low down, I thought – took me off ‘light diet’ and sent me into the ‘bull ring’ for meals.
1928		(con. WWI) E. Blunden Undertones of War 3: I associate it [i.e. Étaples], as millions do, with ‘The Bull-Ring’, that thirsty, savage, interminable training-ground.
1932		(con. WWI) L. Mann Flesh in Armour 8: The bull-ring had failed to cure the slouch acquired on the heavy soil of his father’s farm.
1968		G. Slatter Pagan Game (1969) 86: The women on the staff hate us being out here on the bullring while they have to cope with the girls.